1. The Field of the Invention
The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention is directed to an improved method of alloying a semiconductor device during the manufacture thereof
2. The Relevant Technology
Hydrogen alloying, or annealing in a hydrogen atmosphere, is used to heal damage caused to the lattice structure of the crystalline semiconductor substrate by the various processes used to form circuit structures. Hydrogen, in the alloying process, forms bonds with damaged areas of the substrate, tying up dangling bonds of substrate atoms and improving the electrical properties of the substrate.
Hydrogen alloying is typically employed near the end of an integrated circuit fabrication procedure, after all circuit devices have been formed. Some typical structures present on a semiconductor substrate during such post-metal alloying are shown in cross section in FIG. 1.
FIG. 1 shows a partial cross section of a semiconductor device. Semiconductor substrate 12, typically a silicon substrate, has an isolation region 14, typically field oxide, which has been grown thereon. Wordlines 16 each enclosed in spacers 18 are formed over substrate 12 and isolation region 14. A thin etch-stop and sealing layer 20, typically silicon nitride, is present on substrate 12 and isolation region 14 except where plugs 24 contact substrate 12. Plugs 24 are formed of an electrically conductive material and extend from substrate 12 up through a first dielectric planarization layer 22. A capacitor structure including capacitor plate 26, thin dielectric layer 28, and capacitor plate/ground line 30 is formed in contact with one plug 24. In contact with the other plug 24 is a conductive-material via 34, typically formed of metal, which extends upward from the other plug 24 through a second dielectric planarization layer 32 to a conductive-material bitline 36, also typically formed of metal.
The typical hydrogen alloying step is performed upon structures identical to or similar to those shown in FIG. 1. Sealing layer 20 is relatively impervious to diffusion of various dopants, including hydrogen. Other structures formed on substrate 12 can also impede the diffusion of hydrogen somewhat. Thus, the path hydrogen must take to diffuse into substrate 12 typically takes the form of path P shown in FIG. 1. The hydrogen must typically pass through or around bitline 36, along via 34 and plug 24 and down into substrate 12 to alloy substrate 12 in region R. As circuit density in semiconductor devices increases, diffusion of hydrogen along path P of FIG. 1 becomes lengthy and more difficult, such that adequate hydrogen alloying of substrate 12 cannot be achieved. Thus an improved hydrogen alloying method is needed.
An object of the present invention is to provide a method of alloying a semiconductor device, said method providing adequate alloying even in highly dense devices.
Still another object of the present invention is to provide a rapid method of alloying a semiconductor device.
Still another object of the present invention is to provide a method of alloying a semiconductor device in situ with existing process steps.
In accordance with one preferred method of the present invention, alloying is performed upon a substrate on which wordlines enclosed in spacers have been formed, with the substrate exposed between the wordlines. A thin sealing layer is then deposited over the substrate and the wordlines, the sealing layer helping to maintain the hydrogen in the substrate. The hydrogen employed in alloying the substrate is optionally monatomic hydrogen.
According to another preferred method of the present invention, alloying is performed with monatomic hydrogen at a post-metal alloying step. Alloying with monatomic hydrogen may also be used at other process steps as desired.
Alloying while the substrate is still directly exposed can allow for a greater alloy concentration. The thin sealing layer deposited thereafter helps maintain the alloy concentration, such that subsequent damage to the substrate may be repaired in situ.
Alloying with monatomic hydrogen increases the diffusivity and reactivity of the hydrogen, allowing shorter process times and lower temperatures to achieve the same alloying effect.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.